Cell cultures of Arabidopsis thaliana (cv. Columbia) were used to screen for early alterations in gene expression as a response to altered gravitational fields. Genes of interest were selected from a larger group whose expression was altered under hypergravity (microarray study; M. Martzivanou and R. Hampp, Physiol. Plant. 118: 221-231, 2003). Transcriptional changes of these genes were studied within a time frame of up to 10 min of exposure to microgravity in a sounding-rocket experiment, to clinorotation (random positioning machine), and to hypergravity (8 g). We could identify a set of nine genes (mainly components of signaling chains) with increased transcript levels after about 6 min of exposure to microgravity. As clinorotation and hypergravity treatment did not alter the respective transcript amounts, we assume that the identified genes could be involved in a microgravity-related response.